Frequency-dependent selection, as seen in the case of the scale-eating fish in Lake Tanganyika, tends to
A) eliminate rare alleles and favor whichever allele is initially most frequent.
B) maintain two phenotypes in a dynamic equilibrium in a population.
C) produce random changes in allele frequencies.
D) stimulate new mutations.

Question

Quizplus · Accepted Answer

Frequency-dependent selection maintains two phenotypes in a dynamic equilibrium such that neither phenotype becomes too rare or too common. In the case of the scale-eating fish in Lake Tanganyika, the advantage of each phenotype depends on the frequency of the other phenotype. Thus, if one phenotype becomes too common, the advantage shifts to the other phenotype, which then becomes favored by selection. This cycling of advantages and disadvantages results in a stable polymorphism with both phenotypes present in the population.

Frequency-Dependent Selection, as Seen in the Case of the Scale-Eating